1. Field of the Invention
The present invention relates to a testing circuit, and particularly to a testing circuit for a data interface.
2. General Background
The use of a Universal Serial Bus (USB) interface for coupling a peripheral device, such as a modem, a digital camera, a scanner, a keyboard, and/or a mouse, to a host computer/controller has become well known. Moreover, the maximum transmission rate of the USB interface is continually increasing. For example, while the USB 1.0 standard provided a transmission rate of 12 Mb/s, the USB 2.0 standard provides for a transmission rate of 480 Mb/s. As the speed of data transmission continually increases, it is becoming increasingly important and yet, more difficult to accurately test the performance of the USB interface. In general, a power supply provides a 5V voltage to the USB interface. The USB 2.0 standard requires the working voltage of the USB interface be between 4.75V and 5.25V. So, when the USB interface is coupled to a peripheral device, if the voltage of the USB interface is lower than 4.75V, the USB interface cannot provide a normally functioning connection between the peripheral device and the host computer.
What is needed is a testing circuit for a data interface which can detect whether a working voltage of the data interface reaches the minimum voltage with different loads.